Dies which are used in presses for stamping metal parts must be replaced from time to time, because of die wear and because the same press will be used at different times to produce different parts. Die changes are relatively frequent at automobile stamping plants because of the number of different metal parts in an automobile. Die changes must be even more frequent at stamping plants which produce parts for more than one model of automobile. Replacement of a die results in lost time because the press must be shut down while a die is being changed. Additional concerns in replacing a die are safety and minimization of physical labor. The latter is a concern because most automobile parts are large, requiring large, heavy dies for their manufacture.
Up until now one way to remove a die from a press was to either push it out using a fork lift from the rear and bringing a crane from above to pull simultaneously while the fork lift is pushing from the rear, using some type of blocking or support to the front of the press on which to bring the die. Other ways of removing dies involve the use of a movable bolster on which the die is mounted. The die and the bolster are removed as a unit from the press and the die is taken off the bolster outside the press. For example, the bolster may be a rolling bolster which runs on tracks that go into the side of the press itself; the rolling bolsters are hydraulically activated, wheels drop down, the entire bolster itself rolls to the side of the press where a crane can pull it off and another die put in place back on the bolster. The bolster is then pushed back into the press, the wheels are raised and the bolster put back in place and bolted back down. U. S. Pat. Nos. 3,422,660 to Countess, Jr. et al and 3,986,448 to Sigfried et al illustrate such an arrangement.
Still another way for removing a die from a press is shown in U. S. Pat. No. 3,831,427 to Lee. According to this patent, a die and a die supporting shoe are moved as a unit from the press to a press feed table which is situated alongside the press. The table has two parallel horizontal table members and a single hydraulic or pneumatic actuator which is attached to the die shoe to move the same between the press and the feed table. While this apparatus is simpler than most arrangements which use moving bolsters, it still has certain disadvantages including a press feed table that is permanently in place, taking up space which might otherwise be used for manufacturing purposes.
Trying to pull a die out with chains and fork lifts takes too long, is too dangerous and is not cost efficient. The movable bolsters have too many moving parts which can wear. The wear factor on the wheels (where used) and on the tracks is extensive and the wheels are extremely expensive to replace.